1. Field of the Invention
This invention relates generally to waste lagoon and landfill constructions, and more particularly to compositions and processes for constructing low-permeability barriers for waste lagoons and landfills.
2. Description of the Relevant Art
The proliferation and filling of waste disposal sites such as waste lagoons and landfills has raised increasing concern regarding the long term effects of degradation of the landfill on the surrounding environment. Of primary concern is the effect of water drainage through the landfill, which drainage will leach hazardous substances from the landfill material and will transport these substances to the surrounding environment. Strict government regulations have therefore been promulgated which require the construction of barriers around the landfill area, and as a final cover or cap over the waste lagoon or landfill site. These requirements primarily relate to the permeability of the barrier to water and other liquids, which permeability should be minimized. Water-resistant materials currently used as liners include polyethylene. A cap or the final cover must also be engineered to minimize infiltration of precipitation into the landfill, and therefore must be no more permeable than a liner system. Any potential disruption of continuity and functionality of the cover must be minimized. It is therefore preferable to provide a cover design which will have good drainage, minimum erosion, and require minimum maintenance.
Final covers for waste lagoons and landfills commonly have three layers: a vegetated top cover, a middle drainage layer and a low-permeability bottom layer. The low-permeability bottom layer is usually composed of two components, including an upper geomembrane and bedding material of well graded sand for drainage. A lower component can include a layer of compacted clay, sometimes two or three feet thick and having a hydraulic conductivity of no more than 1.times.10(-7) centimeters per second. The low permeability of the material will reject the transmission of fluid into the landfill, will minimize the generation of leachate, and will also minimize the filling of the landfill with leachate (the "bathtub" effect). Current low-permeability barriers are usually quite thick, often two to three feet, and can significantly decrease the available volume in the waste disposal site for the actual disposal of waste materials.
The geomembrane is expected to deteriorate in time, after which the compacted clay layer will be entirely responsible for the prevention of infiltration. Settlement and frost heaving are two occurrences that will disrupt the functionality of this layer. The system should therefore be designed to take into consideration the long term settlement, and differential settlement, of the material under the cap, and the layer should be placed below the average depth of frost penetration in the area.
The low permeability layer will sometimes be used as an interim cap without a vegetative layer and a drainage layer. In these instances, it is additionally necessary to design the cap to minimize crack development and erosion.